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Ruthenium(IV) oxide
Ruthenium(IV)-oxide-unit-cell-3D-vdW.png
IUPAC name
Other names Ruthenium dioxide
Identifiers
CAS number 12036-10-1 Yes check.svgY
Properties
Molecular formula RuO2
Molar mass 133.07 g/mol
Appearance blue-black solid
Density 6.97 g/cm3
Boiling point

1200 ºC subl.

Solubility in water insoluble
Structure
Crystal structure Rutile (tetragonal), tP6
Space group P42/mnm, No. 136
Coordination
geometry
Octahedral (RuIV); trigonal planar (O2–)
Hazards
MSDS External MSDS
EU Index not listed
Flash point Non-flammable
Related compounds
Other anions Ruthenium disulfide
Other cations Osmium(IV) oxide
Related ruthenium oxides Ruthenium tetroxide
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Ruthenium(IV) oxide (RuO2) is a black chemical compound containing the rare metal ruthenium and oxygen. The most often used O2 catalyst is ruthenium(IV) oxide, however care must be taken since hydrates of this oxide exist.[1]
RuO2 is generally used as a catalyst in various industrial applications or an electrode in electrochemical processes. RuO2 is highly reactive with reducing agents, due to its oxidizing properties.

Contents

Structure and physical properties

Ruthenium(IV) oxide takes on the rutile crystal structure[2][3], similar to titanium dioxide and several other metal oxides. Due to its structure, ruthenium(IV) oxide easily forms hydrates.

Ruthenium(IV) oxide is a (nearly black) purple crystalline solid at room temperature. The hydrates of RuO2 have a blue color to them.

Ruthenium oxide has great capacity to store charge when used in aqueous solutions.[4] Average capacities of ruthenium(IV) oxide have reached 650 F/g when in H2SO4 solution and annealed at temperatures lower than 200 ºC.[5] In attempts to optimise its capacitive properties, prior work has looked at the hydration of ruthenium oxide, its crystallinity and particle size.

Preparation

There are various ways in preparing ruthenium(IV) oxide. The following processes described below are for preparing RuO2 as a film.

1. The chemical vapor deposition (CVD) of RuO2 from suitable volatile ruthenium compounds.[6]

2. The pyrolysis, or heating of ruthenium halides, suitably deposited on the substrate by spraying on the heated substrate a solution of the halide . The most commonly used halide is ruthenium(III) chloride to form RuO2.
This technique has in fact been developed by Schafer for the preparation of nearly stoichiometric RuO2 single crystals.[7]
Both process follow the same reaction mechanism:

Ru+(IV) + O2 (heat)→ RuO2
High temperature flashes of heat up to 1500oC can remove all oxides and contaminants, and form a new oxide layer on the ruthenium.

3. Another way to prepare RuO2 is through electroplating. Films can be electroplated from a solution of RuCl3.xH2O. Pt gauze was used as the counter electrode and Ag/AgCl as the reference electrode.[8]

Uses

RuO2 is extensively used for the coating of titanium anodes for the electrolytic production of chlorine and for the preparation of resistors or integrated circuits.[9][10]

Ruthenium(IV) oxide is a versatile catalyst and doping agent. hydrogen sulfide can be split by light by using a photocatalyst of CdS particles doped with ruthenium(IV) oxide loaded with ruthenium dioxide.[11] This may be useful in the removal of H2S from oil refineries and from other industrial processes. The hydrogen produced could be used to synthesize ammonia, methanol, and possibly fuel a future hydrogen economy.

Ruthenium (IV) oxide is being used as the main component in the catalyst of the Deacon process which produces chlorine by the oxidation of hydrogen chloride.

Oxidative catalyst

RuO2 by itself is a poor catalyst because without the presence of a hydrate its surface area is greatly decreased. To get pure ruthenium(IV) oxide, it needs to be annealed at 900 ºC. The best catalyst for electrochemical processes is to have some hydrate present, but not a completely hydrous one.[12] RuO2 can be used as catalyst in multiple reactions. Such noteworthy reactions are the Fischer-Tropsch process and fuel cells.

References

  1. ^ Mills, A.; Chem. Sot. Rev.,1989, 18, 285.
  2. ^ Wyckoff, R.W.G.. Crystal Structures, Vol. 1. Interscience, John Wiley & Sons: 1963.
  3. ^ Wells, A.F. (1975), Structural Inorganic Chemistry (4th ed.), Oxford: Clarendon Press  
  4. ^ Matthey, Johnson. Platinum Metals Review. 2002, 46, 3, 105
  5. ^ Kim,Il-Hwan; Kim, Kwang-Bum; Electrochem. Solid-State Lett., 2001, 4, 5,A62-A64
  6. ^ Pizzini, S.; Buzzancae, g.; Mat. Res. Bull., 1972, 7, 449-462.
  7. ^ Schafer, H., Z.an.allg. Chem. 1963, 319, 327
  8. ^ Leea, Se-Hee; Liu, Ping.; Solid State Ionics 2003, 165, 217-221.
  9. ^ De Nora,O.; Chem. Eng. Techn., 1970, 42, 222.
  10. ^ Iles, G.S.; Platinum Met. Rev., 1967,11,126.
  11. ^ Park, Dae-chul; Baeg, Jin-ook., U.S. Pat. Appl. Publ., 2001,6 pp.
  12. ^ Mills, A.; Davies, H.; Inorganica. Chimica. Acta., 1991, 189, 149-155

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